What Does BPA Have to do With Metabolism, Mazes, and My Mom?

Last week my mom called me out of the blue with a question on chemicals. You see, in my family, we make (and eat) a lot of kimchi—that spicy, wonderful, fermented cabbage that is ubiquitous in Korean cuisine. For my entire life, we’ve been using the same hard plastic containers to store and ferment kimchi in the basement fridge. My mom was calling me because those containers were getting pretty old and she wanted to replace them. She was wondering whether she should pay a bit more to buy kimchi containers that were explicitly labeled “BPA free.”

Bisphenol A, or BPA for short, is a compound that you’ve probably heard a lot about. I vaguely remember hearing about it when I started high school. At the time everyone and their parents were swapping out their old water bottles for those labeled as “BPA free.”

The questions swirling around BPA have made a reappearance in my life as a fellow working on chemicals issues at EDF. Among other chemicals, EDF has been following the science behind BPA (see here, here, and here) for quite some time.

So what’s the big fuss? Well, first, there is widespread exposure to BPA. The biennial CDC NHANES biomonitoring survey indicates that nearly all Americans are exposed to BPA. Indeed, BPA can be found in everyday products including receipts, canned food lining, and plastic water bottles. BPA is also an endocrine disrupter — a chemical that mimics a natural hormone and can interfere with the normal function of the very important endocrine (i.e., hormone) system. Indeed, numerous animal and human studies (see here, here, and here for example) strongly suggest that BPA can have some pretty awful effects, ranging from impacts on cardiovascular health and neurological development to reproduction and cancer.

Two recently published studies have added more insight into the potential metabolic and neurodevelopmental effects of BPA.

BPA and metabolic effects

A new study conducted jointly by researchers at the University of Toulouse in France and Tufts University in Boston examined the long-term metabolic effects of perinatal (around birth) BPA exposure. The researchers conducted their study by exposing pregnant laboratory rats to various low daily doses of BPA: 0, 0.25, 2.5, 25, and 250 micrograms per kilogram of body weight (µg/kg-bw). The lower two doses are below, and the upper two doses are above, the current FDA daily “safe” intake level of BPA for humans (5 ug/kg-bw) The researchers then took the litters (offspring) of these rats, raised them to adulthood, and analyzed differences in the metabolomes (the complete make-up of small molecules and metabolites) of the offsprings’ blood and livers.

Using new statistical techniques, researchers were able to show that the different doses of BPA administered to pregnant rats led to differences in the blood and liver metabolomes of their offspring that persisted into adulthood. Interestingly, the authors found changes in levels of compounds involved with providing the body’s energy (e.g., glucose, lactate, and fatty acids.

In addition, by analyzing a subset of the metabolites, the authors found that BPA affected a set of biochemical pathways linked to the ability of cell membranes to function as neurotransmitters. This new suggests a potential link between BPA exposure, cell signaling and neurodevelopment.

BPA and spatial learning

Another study by researchers at the University of Missouri, the National Center for Toxicological Research at the FDA, and Texas A&M University study the effects of BPA exposure on spatial learning in laboratory rats —specifically, the ability to remember landmarks and visual cues from one’s surroundings. In their study, groups of pregnant rats were given various daily doses of BPA: 0, 2.5, 25, and 2500 μg/kg-bw. After birth, the offspring of these rats continued to receive the same daily doses of BPA as their mothers.

At approximately three months of age, researchers evaluated the offspring’s spatial learning abilities using a Barnes maze. The Barnes maze consists of a large table with 20 circular holes cut around its edges. Underneath one of the holes is a small box in which a rat can take shelter. The idea is that, placed on the exposed table under light, the rat will try to quickly locate the correct sheltered hole and will learn where that hole is relative to other visual landmarks in the test room. By measuring the amount of time it takes the rats to find the shelter hole after a week of training, researchers can assess whether rats are having trouble learning the spatial cues set around the room.

In this study, researchers found that female rats that had been exposed to the highest levels of BPA had greater difficulty remembering where the shelter hole was relative to the lower dose groups. Curiously, they did not find this effect in males, which suggests the need for further research regarding sex-specific effects of BPA on neurodevelopment.

Advice to Mom?

So what did I tell my mom to do about her kimchi containers? I told her to switch to glass if she could, but my mom’s getting old and lifting those big glass jars of kimchi isn’t easy. Unfortunately, I couldn’t tell her that those lightweight plastics were safe without a slew of qualifiers. So when I get home for Thanksgiving, there’ll probably be a mountain of kimchi (which I will finish, some way or another), some inspections of our containers, and a trip to the store to check out our options.